The invention relates to a process and equipment for conveniently handling a filament in the form of an optical fiber during multiple processing operations that may be at least partially automated. More particularly the invention relates to compact handling of optical fibers during manufacturing operations to include Bragg gratings in at least a portion of their length via a series of manufacturing operations including mechanical stripping, acid stripping, Bragg grating writing, and optical fiber recoating and testing.
Glass has been used for centuries as a material of choice in a variety of scientific and domestic applications. From the early use of prismatic glass for separating light into its component colors, glass has been widely used in optical devices that control or adjust the properties of light beams. A recent and rapidly expanding application of the light modifying properties of glass structures involves the drawing of fine filaments of highly purified glass, more commonly referred to as optical fibers, that direct light signals between light transmitting and receiving locations.
During the late 1970s utilities began using optical fiber installations for internal communication, and by the early 1980s, a number of small optical fiber networks were installed. The use of such networks has been growing ever since to replace existing coaxial cable systems. Advantages provided by optical fiber communications networks include lower cost, the use of fewer signal repeaters to correct for signal distortion, and a higher signal carrying capacity than coaxial cable networks.
The capacity of fiber optic systems continues to increase. In 1980, the first systems could transmit 45 megabits per second. Current systems transmit up to 5 gigabits per second. So extensive is the modern use of optical fiber networks that fiber optic networks have essentially replaced all transcontinental copper cable networks and entirely new networks are being created continually. One prediction claims that every continent in the World will become part of a global fiber optic network.
A fiber optic system includes three main parts of transmit circuitry and light source, light detector and receiver circuitry, and fiber. The transmit circuitry converts electronic signals to modulate a light source that generates light signals for transmission. Connection from the light source to a length of optical fiber facilitates transmission of light signals for distances covered by the optical fiber. Attachment of light detector and receiver circuitry at the terminal end of a fiber produces a communication link The use of multiple communication links provides extended networks of transmitters and receivers.
Interconnection of fiber optic networks requires high precision devices in the form of optical connectors that join optical fibers to peripheral equipment and other optical fibers while maintaining adequate signal strength. In operation an optical connector centers the small fiber so that the light gathering core lies directly over and in alignment with a light transmitting source or another fiber. Sections of optical fiber may also be spliced together using mechanical splicing or fusion splicing techniques.
Special features may be built into selected, relatively short lengths of optical fibers to be spliced into fiber optic networks. A fiber Bragg grating represents a light-modifying feature that may be introduced or written into an optical fiber by simple exposure to ultraviolet light. The ability to write such gratings leads to a variety of devices. For example, Bragg gratings may be applied in telecommunications systems to control the wavelength of laser light, to introduce dispersion compensation, and, in the form of long period gratings, to modify the gain of optical fiber amplifiers. Fiber optic applications of fiber Bragg gratings, outside of telecommunications, include spectroscopy and remote sensing.
The process of introducing special features such as Bragg gratings into an optical fiber may include a number of steps requiring handling of relatively short lengths of optical fiber during a series of manufacturing operations. An optical fiber typically requires removal of protective coatings before changing the physical characteristics of the fiber to include a Bragg grating. After writing a Bragg grating, the fiber may be annealed and recoated.
Little has been revealed about the automation of processes to alter the characteristics of a fiber to provide it with a refractive index grating. Some evidence exists of individual processing steps but not of a type that may be readily incorporated in an automated sequence. Fiber loading for example is described in U.S. Pat. No. 5,988,556. This patent refers to automated winding of a continuous length of fiber from a fiber supply onto first and second sections of a shipping spool. The winder comprises a first device that collects a first portion of a continuous length of fiber and winds it onto the first section of the spool, and a second device for winding a second portion of the continuous fiber onto the second section of the spool. There is no evidence to show that the spooled fiber has a use other than as a shipping package. U.S. Pat. No. 6,027,062 describes an automated winder including fiber supply and collecting devices that move a fiber to a threading device that automatically threads the fiber onto a spool. This is similar to the goal of U.S. Pat. No. 4,511,095 to form of a coil of fiber wound onto a bobbin or similar structure.
The use of stackable cassettes for handling and organizing optical fibers is well known, particularly for storage of lengths of spliced fibers. Cassettes typically comprise shallow dish-shaped holders and enclosures for containment of loosely coiled optical fibers. Loose optical fiber coils do not have the same compact structure as spooled optical fibers. An intermediate form of coiled fiber, described in U.S. Pat. No. 5,894,540, may be produced using an assembly for holding a length of filamentary material in a wrapped configuration with a minimum bend radius. The filament or fiber may be wrapped around spools attached to a support plate. Adjustment of the spacing between spools removes slack from the fiber wrapped around them. Fiber cassettes and related fiber holding assemblies place loose fiber in a tidy condition for storage, usually following interconnection of lengths of optical fiber. U.S. Pat. No. 6,088,503 confirms the use of optical fiber cassettes as holders of optical fibers before, during and after splicing. The patent describes a clamping tool designed to align and hold a pair of fiber ends in preparation for optical fiber splicing.
Cassettes and related fiber organizing assemblies provide tidy storage for optical fibers around connected and spliced sections of optical fiber. There appears to be no evidence of such storage containers used for processing organized lengths of optical fiber during the manufacture of optical fiber devices. One manufacturing process requires the removal of protective buffers and coatings to reveal the bare surface of an optical fiber. Several processes are known for removing protective layers, such as buffers and coatings, from the surface of optical fibers. They include mechanical stripping, chemical stripping and thermal stripping.
Mechanical stripping of optical fibers and related coated filaments requires careful positioning of sharp tempered metal blades to expose a bare surface portion of a fiber without cutting or scratching or otherwise physically damaging the fiber surface. Known methods of mechanical stripping relate to cutting blade design and how a coating may be removed from the surface of a fiber. The predominant use of mechanical stripping involves the removal of protective layers from the ends of optical fibers, insulated wires and related filaments, prior to joining the filament ends together. U.S. Pat. No. 4,434,554 describes an optical fiber stripping device including a flat base having a number of fiber receiving channels of suitable depth to ensure only removal of a buffer coating from each fiber, when a blade penetrates the coating. The blade moves parallel to the axis of a fiber or group of fibers using a paring action to remove protective material. Channel size, based upon fiber diameter determines the selection of a flat base to provide a device that strips a fiber end without damaging the fiber itself.
One way to avoid damage to the bare surface of an optical fiber requires the use of blades designed to penetrate the protective buffer or fiber coating without reaching the fiber surface. Suitable blades have a substantially semicircular sharpened edge of a radius slightly larger than the radius of the bare optical fiber. Two opposing blades, penetrating the protective layer around the fiber, interfere with each other before the cutting edges reach the fiber surface. After penetrating a protective layer, close to the end of a fiber, movement of the blades parallel to the fiber axis displaces a section of the layer to provide a bare fiber end untouched by the blades. United States Patents, including U.S. Pat. Nos. 4,630,406, 5,269,206, 5,481,638, and 5,684,910, describe the manufacture and design of blades for cutting insulation from e.g. insulated electrical wires and optical fibers. Successful mechanical stripping using such blades may require additional treatments, including softening the protective layer as in U.S. Pat. No. 5,481,638 requiring a chemical filled chamber first to soften an encapsulating layer then to clean plastic material from the blades after stripping. U.S. Pat. No. 5,684,910 teaches an optical fiber having improved mechanical strippability. The improvement includes the use of a frangible boundary layer between a fiber coating and a buffer to facilitate separation from the bare fiber. Previous teachings include initial blade movement perpendicular to a filament axis, to penetrate a coating, followed by movement parallel to the filament axis to expose bare filament ends by displacement of protective layers.
Chemical stripping may be used as an alternative to mechanical stripping for preparing bare fiber ends. United States Patents, U.S. Pat. Nos. 4,865,411 and 4,976,596 deal with controlled removal of coating, by gradual withdrawal of a coated fiber from a chemical bath, to produce a contoured shallow taper adjacent to the bare glass fiber surface. A fixture, according to U.S. Pat. No. 5,451,294 provides support while dipping the end of a coated optical fiber into a chemical bath to dissolve coating from the end. Chemical stripping methods include common problems related to the handling of chemicals especially, as in this case, when the chemical strippers involve corrosive liquids.
Hot gas stripping may be used instead of mechanical or chemical stripping. One example of this process, described in U.S. Pat. No. 6,123,801, uses a hot inert gas to melt buffer coating and blow it from the surface of an optical fiber. The process requires high pressure gas streams and temperatures in the region of 800xc2x0 C. to strip coating from the fiber. U.S. Pat. No. 5,939,136 describes a process for preparing optical fiber devices including thermal removal of a coating from an optical fiber, preferably performed using a heated gaseous stream.
A reason for removing protective buffers and related coatings from optical fibers is the need to change the characteristics of the fiber such as by writing of a refractive index grating, also known as a Bragg grating, in the core of an optical fiber. Refractive index changes occur during exposure of a bare fiber to radiation from an ultraviolet laser or similar exposure device. The majority of protective coatings for optical fibers absorb the fiber modifying radiation. This explains the need to remove the coatings before writing a refractive index grating.
Without further processing, an optical fiber including a refractive index grating also has a bare portion that requires application of protective coatings before use in an optical fiber device. The widely accepted method for recoating bare sections of optical fibers involves special coating molds. Methods similar to those used to coat drawn fibers, during their manufacture have also been described.
A recoating mold, described in U.S. Pat. No. 4,410,561, provides a coated optical fiber using a split mold die structure. The size and design of a cavity formed by the closed mold provides space that becomes filled during injection of curable, protective, fluid recoating compositions. It is desirable to avoid entrapment of air inside the mold since this could lead to a defective recoated fiber section. Complete filling of a mold cavity may involve intentional application of pressure. U.S. Pat. No. 5,022,735 uses a screw type plunger to pressurize recoating fluid injected into a conventional recoating mold. Some recoating molds include curing means to provide finished recoated sections of optical fibers. U.S. Pat. No. 4,662,307, for example, uses a split mold including an injection port and UV light port through which light passes to cure recoating compositions. The curing process requires multiple light sources.
Application of coatings to an optical fiber drawn from a pre-form typically places the emerging fiber in a vertical orientation. As it travels downward, the fiber may pass through a reservoir of coating fluid before exiting through an orifice sized to the desired external diameter of the coated fiber. It is possible to apply such a process to recoating of bare sections of optical fiber including a Bragg grating, as taught in U.S. Pat. No. 6,069,988. Upon exit from the orifice, the fiber moves past a source of curing radiation. The curing radiation differs from the radiation used for writing the Bragg grating so as not to destroy or change the characteristics of the grating.
There is evidence in Japanese Patents JP 60-122754 and JP 61-40846 for spraying protective plastic coatings on optical fibers exiting a draw tower. Coverage of the full circumference of the optical fiber requires the uses of either multiple spray heads or special spray containment shrouds. The use of multiple spray heads deposits only a fraction of the spray on the surface of the drawn fiber while the use of special shrouds involves complicated threading of a fiber.
Each point in the processes, of fiber stripping, modifying and recoating, requires care to prevent damaging the fragile optical fiber. Damage to optical fibers may occur by physical contact or exposure to tensile, torsional, twisting, and bending stresses. Excessive bending can change the optical characteristics of a fiber. Failure to meet required optical characteristics leads to rejection of an optical device and increases the expense of device manufacture. A need exists for improved means for handling optical fibers for post draw processing, to reduce incidence of damage thereby reducing the cost and increasing the yield of optical fiber devices.
The present invention satisfies the need for effective and compact handling of filamentary materials during manufacturing operations including process steps that produce structural and related changes in the filament. When applied to optical fibers, an article, also described herein as a filament organizer, provides compact containment of an optical fiber. The filament organizer allows relatively precise positioning of at least a portion of an optical fiber to facilitate processing of optical fibers related to optical couplers, fused couplers and tapered fiber devices and the like. Optical fiber modification may also refer to actions taken to change the inherent characteristics of an optical fiber or to incorporate an optical fiber into a functional assembly. The inherent characteristics of an optical fiber change with adjustment of its refractive index properties, as in the formation of a variety of fiber Bragg gratings. Incorporation of an optical fiber into a functional assembly provides useful devices such as temperature compensated fiber Bragg gratings. Refractive index changes and functional assembly production, according to the present invention, use a filament organizer that distributes an optical fiber between a lockable spool and a rotary spool to expose a central portion of a fiber to be modified.
A computer controlled, or otherwise programmed, fiber dispenser may be used to load a prescribed amount of a substantially twist-free optical fiber between a pair of spools mounted on a common axis. After fiber loading the spools are separated, with fiber extending between them, and mounted to a filament organizer for fiber storage and further processing. Use of computer controlled dispensing, combined with a filament organizer, allows accurate consistent loading and organization of a selected length of optical fiber within the boundaries of the filament organizer. Control of the loading process allows the production of numerous holders containing approximately equal lengths of fiber, organized in similar fashion. After successful loading of an optical fiber, a filament organizer provides a convenient article for handling the fiber through process operations required for the manufacture of optical fiber devices. Preferably the filament organizer includes means for applying a tension force between about 50 g to about 100 g to the filament held therein.
A variety of devices use optical fibers that have been structurally modified to include in-line optical waveguide refractive index gratings in at least a portion of their length. Physical property variation of gratings allows them to be tailored for specific applications. In one embodiment, the present invention provides a fiber Bragg grating obtained via a series of manufacturing operations including mechanical stripping of an optical fiber, acid stripping, pigtailing, optical fiber Bragg grating writing, annealing and optical measurement followed by recoating and testing. The final step of testing, including fiber proof testing, confirms attainment of performance requirements desired of an optical fiber Bragg grating.
Each operation or step of the manufacturing process requires attachment of one or more filament organizers to one or more filament processors or apparatus designed specifically to accomplish a designated step. This requires that the size and shape of a filament organizer include aspects of design allowing convenient connection with several filament processors. As well as making suitable connection with several types of filament processors, an important requirement of a filament organizer is containment of a prescribed length of filament that may be up to several meters in length. Preferably, in the case of an optical fiber, a filament organizer holds most of the length of a filament on a pair of spools leaving a portion of filament available for processing. A spool holds two sections of optical fiber wound in the same direction on separate sides of a divided spool core. One section of fiber extends between a pair of spools while the other section of optical fiber provides a pigtail portion that may be readily unwound from each spool. There is a pigtail section at each end of a continuous length of optical fiber.
After winding a continuous length of optical fiber between a pair of spools and positioning the spools on a support board, fiber handling may proceed with reduced expectation of damage to the fiber. Also the use of a filament organizer allows ready access to a portion of fiber. Ready access to this portion of fiber allows it to be modified initially by removal of protective coatings from its surface and thereafter subjecting it to operations that change its physical and optical properties, as in the writing of a fiber Bragg grating into a bared portion of optical fiber. A filament organizer allows reproducible positioning of that portion of an optical fiber that will be modified. Reproducible positioning leads to predictable results of filament or optical fiber modification by operations that may be conducted using a process where at least several of the steps may be automated.
As indicated previously, a filament organizer provides a portion of filament or optical fiber suitably positioned for processing. Formation of an optical fiber Bragg grating according to the present invention requires that any polymeric protective coating, also referred to herein as a buffer coating, should be removed prior to the writing of the fiber Bragg grating. The coating may be removed using liquid or mechanical or thermal stripping.
An optical fiber covered with a single polymeric layer, referred to herein as a primary buffer, may require only liquid stripping using concentrated acid to remove the buffer. Removal of multiple protective coatings, including primary and secondary buffers according to the present invention, preferably uses a combination of mechanical stripping followed by acid stripping. Acid stripping herein refers to dissolving residual coating material in an acid medium with displacement of the acid using a water rinse and solvent wash applied to at least a portion of the fiber. Initial displacement of coating requires specially designed mechanical stripping equipment that cooperates with a filament organizer for precise positioning of the portion of an optical fiber from which protective coating will be displaced. Mechanical stripping equipment may be designed for conveniently processing one filament organizer or several combined in a single stacked configuration. This results in treatment of one or more fibers at a time depending on the number of filament organizers. Coating displacement, via mechanical stripping, creates gaps to the bare fiber through which acid may subsequently penetrate to more rapidly dissolve coating from the fiber portion.
Removal of coating by acid stripping preferably requires an apparatus that forms a loop of filament for each filament organizer included in a stacked configuration. The apparatus is constructed for formation of individual filament organizer loops having approximately the same size. The plane of each loop parallels that of its nearest neighbors. Acid stripping of one or more fiber loops occurs by immersing the arcuate portion of a loop into an acid bath. The depth of immersion of each loop into the acid bath controls the length of protective coating removed from a fiber to provide an optical fiber having a bare portion stripped to the silica surface of the fiber. Acid stripping provides a bare fiber surface that is substantially free from contaminants.
After all of the fibers in a stacked configuration have been mechanically stripped and acid stripped, the pigtail ends of each fiber are manually unwound and organized into groups using pigtail connectors. Pigtail ends trail about one meter from each end of a filament organizer.
As a further refinement, a filament organizer according to the present invention may include a conventional optical fiber connector for terminating optical fiber ends on the surface, and within the boundaries of the filament organizer. Optical connector termination of fibers reduces the length of pigtail portions of an optical fiber while still providing convenient points of attachment to external optical fiber devices. Compact fiber organization of this type distributes the length of an optical fiber on the surface of a filament organizer without any part of the fiber hanging over the edges of the organizer. Any of a variety of optical fiber device interconnects may be used to reduce the overall length of an optical fiber by shortening the pigtail ends. Reduction in the overall length of an optical fiber translates into cost savings associated with each filament organizer equipped with pigtail to optical fiber connector termination.
Following organization by grouping of pigtail ends each filament organizer in a stacked configuration provides a clean, dry, bare fiber portion ready for positioning in a fiber Bragg grating writing apparatus. After release of tension from a filament held by a filament organizer, the Bragg grating writing apparatus applies a selected tension to the portion of an optical fiber before it is modified to produce a Bragg grating. Production of multiple optical fiber Bragg gratings, having a substantially identical wavelength response, requires precise alignment and application of the same amount of tension to each optical fiber portion loaded into the fiber Bragg grating writing apparatus. Precise alignment of an optical fiber portion with the Bragg grating writing apparatus relies on features built into a filament organizer and the grating writing apparatus respectively for consistent relative positioning of one to the other. Consistent loading and fiber portion tensioning relies upon the use of a voice coil drive mechanism and air suspended bearings that facilitate accurate fine adjustment essentially free from drag.
After placing an appropriate portion of an optical fiber under tension in the fiber Bragg grating writing apparatus, the progress of Bragg grating writing may be monitored by observing a display of the wavelength envelope produced by the writing process. Signal information proceeds from an optical fiber to suitable monitoring equipment through connections between the equipment and pigtail ends of a fiber. This provides feedback of the quality of a grating at the time of writing and represents a convenient decision point for acceptance or rejection a fiber Bragg grating as it is written.
Annealing of fibers takes place in a thermal annealing apparatus and fulfils several requirements upon completion of writing of fiber Bragg gratings. This step of the process proceeds at a temperature of approximately 300xc2x0 C. for a duration of more than about three minutes. The annealing process stabilizes the Bragg grating against wavelength drift for time periods exceeding about twenty to about twenty-five years.
After annealing and optical confirmation that the grating center wavelength meets requirements, the fibers and associated Bragg gratings are ready for recoating before final testing. The recoating operation uses equipment designed for a filament organizer or preferably a stacked configuration of filament organizers according to the present invention. It is possible to use in-mold recoating, spray recoating or an extrusion die coating process to recoat the previously stripped portion of each optical fiber. Injection die coating refers herein to conventional in-mold die recoating. Spray recoating uses multiple passes of an optical fiber between a spray head and a radiation curing source. The extrusion recoating process uses a split die that may be positioned around an optical fiber for application of a curable coating composition around the circumference of the fiber as the extrusion head traverses the length of an uncoated fiber portion. Preferably the die head includes a radiation source and the extruded coating cures by exposure to the radiation source. This allows application of recoating material followed immediately by curing.
Application of recoating material to protect a Bragg grating formed in an optical fiber represents the final processing operation for producing fiber Bragg gratings that may be used in telecommunications and related applications. A final check of the resulting product determines if it passes tensile strength and visual inspection requirements. After successfully meeting requirements, the spools holding a finished optical fiber Bragg grating may be detached from the filament organizer and used for conveniently holding, packaging and transporting the final product. A convenient form of packaging for transportation requires transfer of the full continuous length of a fiber Bragg grating to one spool after removing it from the filament organizer. The design of a spool provides a protective cover for the fiber Bragg grating element following transfer of the full length of optical fiber to one spool.
More particularly, the present invention provides a method for manufacturing an optical fiber refractive index grating. A suitable method comprises the steps of providing a substantially twist-free length of an optical fiber between a first spool and a second spool, for attachment of the first spool and the second spool to a support. The support has a first surface opposite a second surface, to provide a filament organizer including the first spool as a lockable spool and the second spool as a rotary spool. The filament organizer further comprises a tensioner coupled to the rotary spool to apply tension to at least a central portion of the length of an optical fiber disposed between the lockable spool and the rotary spool. Further processing of a fiber under tension includes removing at least a buffer coating from the central portion of an optical fiber before applying a controlled tension to the central portion of an optical fiber. A refractive index grating may then be written by changing the refractive index characteristics of the central portion during exposure of the central portion to an interference pattern of high intensity actinic radiation, to produce the refractive index grating. After formation the grating may be annealed and the resulting fiber device proof tested to confirm desired performance properties.
The method described previously uses a filament organizer, comprising a support having a first surface opposite a second surface and further including organizing mounts joined to said first surface and spacer blocks attached to said second surface. The filament organizer has a lockable spool adjacent to the first surface of the support, a rotary spool adjacent the first surface of the support, and a tensioner attached to the second surface of the support. The tensioner includes a tension wire for attachment to the rotary spool to apply tension thereto to transmit tension to a filament disposed between the lockable spool and the rotary spool. A tension relief assembly allows selective reduction of tension applied to a filament. The tension relief assembly includes the tension wire, providing connection between the tensioner and the rotary spool, a tension wire access, and at least one pulley for aligning the tension wire with the tension wire access. Other parts of the filament organizer include at least one mounting plate integrally formed with the support and extending outwardly therefrom, and at least one guide defining a filament path between the lockable spool and the rotary spool. Further the guide is rotationally mounted on the mounting plate, adjacent to the first surface of the support, to provide spacing of the filament path from the support.
During refractive index grating manufacture a mechanical stripping apparatus displaces resin from a resin covered filament, in the form of an optical fiber, by forming a removable sleeve portion between opposing filament ends. The mechanical stripping apparatus comprises a base that has a first clamp attached to the base to hold a filament at a first location. A second clamp is attached to the base and has a separation from the first clamp and is in axial alignment therewith for holding a filament at a second location. The apparatus includes a first set of cutting blades mounted on the base adjacent to the first clamp. The first set of cutting blades includes a first upper blade and a first lower blade. Each of the upper and lower blades includes an arcuate sharpened edge for cutting into resin around a resin covered filament proximate to the first location. A second set of cutting blades is mounted on the base adjacent to the second clamp such that a distance separates the first set of cutting blades from the second set of cutting blades. The distance between cutting blades is less than the separation between the clamps. The second set of cutting blades includes a second upper blade and a second lower blade with each blade including an arcuate knife edge for cutting into resin around a resin covered filament proximate to the second location. A blade actuator secured to the base, and coupled to the first set of cutting blades and the second set of cutting blades, moves the first upper blade and the first lower blade together. During this movement the sharpened edges penetrate resin around a resin covered filament proximate to the first location. The blade actuator also moves the second upper blade and the second lower blade together for the knife edges to penetrate resin around a resin covered filament proximate to the second location. A biasing component also on the base moves the first set of cutting blades and the second set of cutting blades towards each other during displacement of resin from a resin covered filament to form the removable sleeve portion.
The removable sleeve portion may be formed using a method for displacing resin from a resin covered optical fiber between opposing fiber ends. The method provides a mechanical stripping apparatus comprising a first clamp for holding an optical fiber at a first location, a second clamp having a separation from the first clamp and in axial alignment therewith for holding an optical fiber at a second location. A first set of cutting blades, of the mechanical stripping apparatus, is adjacent to the first clamp for cutting into resin around a resin covered optical fiber proximate to the first location. A second set of cutting blades is adjacent to the second clamp for cutting into resin around a resin covered optical fiber proximate to the second location. A distance separates the first set of cutting blades from the second set of cutting blades. The distance is less than the separation between the first and second clamps. The first set of cutting blades and the second set of cutting blades are adapted for movement towards each other during removal of resin from a resin covered optical fiber to form the removable sleeve portion. Resin displacement further includes clamping an optical fiber in the first clamp and clamping the optical fiber in the second clamp such that the optical fiber is under tension. Operating the first set of cutting blades and the second set of cutting blades, for cutting into the resin, produces the removable sleeve that has a gap at each end thereof. The gap at each end exposes a bare filament portion separating the removable sleeve portion from a tapered transition formed in the resin during cutting of the resin as the first and second set of cutting blades move towards each other.
In another aspect according to the present invention an apparatus may be used to form a loop in a section of a filament prior to chemical stripping of resin from e.g. an optical fiber. The apparatus comprises a container including a front wall having a front guide slot formed therein and a rear wall having a rear guide slot formed therein coplanar and parallel to the front guide slot. The container further includes a floor containing at least one slit formed between and parallel to the front wall and the rear wall. A first filament gripper includes a stationary elastomer roller and a positionable cylinder holding a filament therebetween, at a first location thereof. The stationary elastomer roller is rotatably mounted from the front wall to the rear wall, so that the positionable cylinder is mounted, adjacent to the stationary elastomer roller, between the front guide slot and the rear guide slot for repositioning therein. A second filament gripper includes a movable elastomer roller and a movable cylinder holding the filament therebetween, at a second location. The second filament gripper has a separation from the first filament gripper and has substantially axial alignment therewith. The second filament gripper moves towards the first filament gripper to reduce the separation to bring the first location closer to the second location thereby producing a loop of filament between the first filament gripper and the second filament gripper. The loop of filament extends through a slit to below said floor of the container where it may be introduced into a reservoir having a solvent therein to surround at least a portion of the loop of filament to dissolve resin from the portion of the loop. A loop forming container according to the present invention may be sized to accommodate one or more filament organizers having a filament between a lockable spool and a rotary spool. Steps for forming one or more filament loops using a loop forming container may be included in a process for chemically stripping resin from a resin coated filament, preferably as an optical fiber.
Processing of a filament according to the present invention requires the use of a filament holding fixture comprising a gripper having an open position and a closed position. The gripper further comprises a lower jaw mount, and a lower jaw connected to the lower jaw mount, the lower jaw having a planar surface and an open-ended, V-shaped channel formed therein opening to the planar surface to receive at least a portion of a filament. The filament holding fixture also has an upper jaw mount, and an upper jaw assembly. The upper jaw assembly comprises a support flange attached to the upper jaw mount. The support flange includes a support surface, having a substantially conical recessed portion. A fiber clasp, included in the upper jaw assembly, has a contact face opposite a structured surface. The structured surface includes an open-ended groove of substantially rectangular cross section. There is a substantially conical depressed portion formed in the contact face of the fiber clasp. The open ended groove and the V-shaped channel are in longitudinal alignment to contact at least a portion of a filament when the gripper is in the closed position. A plurality of spring connectors hold the fiber clasp to the support flange. Also, an angular compensator is confined between the recessed portion of the support surface and the depressed portion of the contact face by force produced by the plurality of spring connectors. The angular compensator maintains separation of the support flange from the fiber clasp to allow them to move independently. This leads to fine adjustment of the fiber clasp for applying substantially equal force at points of contact of the open-ended groove and the V-shaped channel with a filament, preferably an optical fiber, held therebetween following movement of the gripper from the open to the closed position.
The present invention further provides a filament tensioning apparatus for releasably securing a filament under tension. The tensioning apparatus comprises a tensioning holder and a pair of grippers. The tensioning holder includes at least one support bar, and a first carriage movably mounted at a first location on a support bar. The first carriage includes an upper surface having a first clamp and a voice coil mounted thereon for movement relative to a support bar. A second carriage is movably mounted at a second location on a support bar such that a separation exists between the first location and the second location. The second carriage includes an upper face having a second clamp and a load cell mounted thereon for movement relative to a support bar. The second clamp is in axial alignment with the first clamp to secure a measured filament portion including a bare portion thereof, located inside a first boundary and a second boundary, between the first clamp and the second clamp. A guide bar extends from the voice coil for contact with the load cell to adjust the separation of the first location from the second location, to change tension applied to the measured filament portion, during activation of the voice coil. The pair of grippers of the tensioning apparatus is in axial alignment with the fist clamp and the second clamp, to substantially immobilize the bare portion of the measured filament portion. A filament tensioning apparatus according to the present invention may include a coupling for attaching a filament organizer to position a filament, preferably an optical fiber, to be held between the first clamp and the second clamp. The filament organizer holds a filament between a lockable spool and a rotary spool.
A resin covered filament having had resin removed therefrom may require coating by a method that uses a filament recoating apparatus according to the present invention. Such a filament recoating apparatus comprises a frame for releasably securing a filament and a carriage mounted on the frame to oscillate between a first position and a second position. The recoating apparatus has a first filament holding fixture mounted on the carriage. A second filament holding fixture is also mounted on the carriage in axial alignment with the first filament holding fixture. The fixtures secure a measured filament portion including a bare portion thereof, located inside a first boundary and a second boundary, between the first filament holding fixture and the second filament holding fixture. At least one spray head is attached to the frame at the first position. A radiation source is attached to the frame at the second position. The measured filament portion moves between the spray head and the radiation source, during oscillation of the carriage between the first position and the second position to place the bare portion to receive a curable coating from the spray head. The spray head applies curable coating from the first boundary to the second boundary. Curing of the curable coating occurs by exposure to radiation from the radiation source. Droplets of curable coating composition may be deflected using a deflector, such as an air-knife, to selectively direct coating composition towards a plurality of bare filament portions of filaments, preferably optical fibers, grouped around a spray head. Different coating compositions may be applied to bare filament portions to provide recoated filaments using a first composition and overcoated filaments by application of a second coating composition over the first coating composition. The resulting filaments include a multilayer coating.
An alternative filament recoating apparatus, according to the present invention, comprises a planar surface and an extrusion coating assembly attached to the planar surface. The extrusion coating assembly comprises a first filament holding clamp and a second filament holding clamp opposite the first filament holding clamp. A measured filament portion including a bare portion thereof, located inside a first boundary and a second boundary, lies between the first filament holding clamp and the second filament holding clamp. A coating head, includes a die plate having formed therein an open ended channel including a wall having a fluid entry and a gas port formed therein adjacent a radiation source. The coating head further includes a cover die plate having formed therein an open ended elongate slot. The cover die plate has a hinged connection to the die plate for rotation of the cover die plate between an open position and a closed position. In the closed position the cover die plate lies adjacent to the die plate and the channel aligns with the elongate slot to form a tubular opening through the coating head to encircle a section of the bare portion. A linear transport mechanism adjacent to the coating head includes a guide rod and a carriage slidably mounted thereon for movement along the guide rod. A connecting rod from the carriage to the coating head provides linear displacement of the coating head during movement of the carriage to move the coating head from the first boundary to the second boundary. Curable fluid may be extruded from the fluid entry while energy from the radiation source cures the curable fluid to recoat the bare portion of a filament.
A method for extrusion coating a filament comprises the steps of providing a filament organizer having an extended filament between a fixed spool and a rotary spool to provide a measured filament portion and a bare filament portion of a filament, preferably an optical fiber. Recoating of the bare portion of a fiber follows attachment of the filament organizer to an extrusion coating fixture comprising a guide rod, a carriage movably mounted on the guide rod. A coating die, including a coating head and a radiation source, is joined to the carriage. The coating head has an opening for directing a curable coating composition to the bare filament portion positioned in a channel formed in the coating die and extending therethrough. A curable coating composition is applied to the bare filament portion to provide a recoated filament portion, followed by exposing the recoated filament portion to the radiation source for radiation curing of the curable coating composition applied to the bare portion.
The terms xe2x80x9cbare fiber,xe2x80x9d or xe2x80x9cbare fiber portion,xe2x80x9d or xe2x80x9cstripped fiber,xe2x80x9d or phrases relating to such terms refer herein to the portion of an optical fiber from which protective coating has been removed to expose the silica surface of the fiber.
As used herein, the term xe2x80x9ccladdingxe2x80x9d refers to the outer layer of an optical fiber, as drawn.
The term xe2x80x9cbufferxe2x80x9d or xe2x80x9cprimary bufferxe2x80x9d refers herein to a polymer or resin layer next to a bare fiber.
A xe2x80x9ccoatingxe2x80x9d or xe2x80x9csecondary bufferxe2x80x9d is used herein to describe a polymer or resin layer next to a buffer or primary buffer.
The term xe2x80x9cresinxe2x80x9d as used herein is a general term describing polymer coverings for filaments particularly optical fibers. Materials used for previously defined buffers and coatings fall within the general term of resin.
The term xe2x80x9cfilamentxe2x80x9d herein refers to a fiber structure, preferably a xe2x80x9csilica filament.xe2x80x9d An optical fiber is a preferred form of filament according to the present invention.
A xe2x80x9ctapered transitionxe2x80x9d describes the preferably graduated conical shape of the portion of buffer layers closest to a bare fiber portion after subjecting a coated optical fiber to mechanical stripping according to the present invention.
The term xe2x80x9cribbonizingxe2x80x9d refers to the formation of a single layer of optical fibers, side by side, as a flat ribbon-like structure that facilitates the joining of ends of multiple fibers for insertion in one end of a fiber optic ribbon connector.
The term xe2x80x9cangular compensatorxe2x80x9d or xe2x80x9cball joint levelerxe2x80x9d as used herein means a self adjusting coupling inserted between parts of at least one jaw of a gripper to achieve optimum positional relationship between the contacting surface of the jaw and an object to apply even pressure over the surface of the object.
The use of a xe2x80x9cnon-contactxe2x80x9d method for recoating bare portions of optical fibers means that no portion of the fiber touches any part of the recoating equipment. This is a benefit of suspending a fiber in a filament organizer that may be readily attached to the recoating apparatus with precise fiber to spray head alignment.
A xe2x80x9csplit sizing diexe2x80x9d is a multi-part fiber recoating head that opens to receive an optical fiber, closes to extrude curable recoating material around the surface of a length of fiber and re-opens to release the coated fiber.
The term xe2x80x9cshroudxe2x80x9d refers to a shield over an ultrasonic spray head to direct a stream of inert gas to entrain and move a cloud of droplets of recoating composition towards a target surface, such as a bare portion of an optical fiber.
The present invention has been developed to provide a process and equipment for conveniently handling a filament in the form of an optical fiber during multiple processing operations that may be at least partially automated as a further benefit to the user. These enhancements and benefits are described in greater detail hereinbelow with respect to the several aspects and alternative embodiments of the present invention.